1. Field of the Invention
The invention relates to a wheel suspension type front fork of a bicycle or another two-wheeler.
2. Description of the Related Background Art
As such a kind of wheel suspension type front fork, a structure such that a supporting pipe and a slide pipe which is slidable along the supporting pipe are provided and an exchangeable hydraulic suspension unit is arranged in the supporting pipe has been known (for example, U.S. Pat. No. 5,580,075).
The conventional hydraulic suspension unit is constructed by: a cylinder filled with oil; a piston in the cylinder, and a pair of piston rods which are respectively coupled with opposite surfaces of the piston and projected from both ends of the cylinder. One piston rod is fixed to a lower edge of the slide pipe and the other piston rod is come into contact through a flange with buffer means as a separate member such as coil spring, rubber elastic member, or the like arranged over the supporting pipe.
However, if a pair of piston rods are provided as a hydraulic suspension unit, since it is necessary to provide oil sealing portions for both ends of the cylinder, the unit becomes expensive by an amount corresponding to the oil sealing portions. When a shock force is applied to the lower piston rod through the slide pipe, the upper piston rod and piston are also elevated upward in the cylinder, so that a volume of the cylinder does not change. Therefore, an air spring using the air cannot be provided in the cylinder.
However, in the supporting pipe, when the buffer means is arranged over the hydraulic suspension unit, since it is difficult to insert the unit from the upper edge of the supporting pipe and position it, hitherto, the unit is positioned and fixed from the lower edge side of the supporting pipe before the slide pipe is assembled.
However, in case of the structure such that the unit is positioned on the lower edge side of the supporting pipe, when the hydraulic suspension unit is exchanged, it is necessary to remove the slide pipe from the supporting pipe. For this purpose, the operation to remove a front wheel, a braking mechanism, and a cable for braking from the slide pipe is necessary and a large troublesomeness and a long time are required for the exchanging operation. Since a lubricant such as a grease or the like is coated onto slide opposite surfaces of the supporting pipe and slide pipe and a dust sealing material for prevention of penetration of water or dust is attached, if the slide pipe is removed, there is a fear such that the dust or the like deposited onto both pipes is deposited onto the slide opposite surfaces and becomes a cause of a defective operation.
As another hydraulic suspension unit, a unit disclosed in Japanese Utility Model Application Laid-open No. 63-199894 is known. According to the structure of such a unit, a coil spring for buffering different from the unit is arranged between a supporting pipe and a slide pipe, and a piston rod of the unit is coupled and fixed in the slide pipe. When the unit is exchanged, therefore, it is necessary to similarly remove the slide pipe from the supporting pipe.
It is an object of the invention to provide an inexpensive wheel suspension type front fork which holds an air spring function and can efficiently perform an exchanging operation.
According to a preferred aspect of the invention, there is provided a wheel suspension type front fork having a supporting pipe which is attached to a steering pipe and a slide pipe which is slidably fitted to the supporting pipe and has a bearing pedestal in an edge portion, comprising
a cap for detachably closing an opening of an edge portion of the supporting pipe and an exchangeable hydraulic suspension unit which is arranged in the supporting pipe,
wherein the hydraulic suspension unit comprises: a cylinder which is exchangeably arranged in the supporting pipe through the opening and in which oil is filled; a piston which is moved in the cylinder and has an oil passage; a piston rod which is attached to the piston and projected from the cylinder and detachably coupled with the edge portion of the slide pipe; and buffer means, arranged in the cylinder, for buffering a shock force which is transferred through the piston.
Since the buffer means such as a coil spring or the like is assembled in the cylinder, it is sufficient to provide one piston rod. In case of providing one piston rod, since a volume of the cylinder is changed by the upward motion of the piston rod, even if an air spring is provided in the cylinder, it normally functions. Further, since only the hydraulic suspension unit in which the buffer means is assembled is enclosed in the supporting pipe, the unit can be inserted or removed from the upper edge of the supporting pipe and positioned.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.